Tags

Sodium

Test/Range/Collection

Physiologic Basis

Sodium homeostasis is crucial for life, and the Na+ level of blood is strictly maintained at a range of 135–145 mM.

Sodium is the predominant extracellular cation. The serum sodium level is primarily determined by the volume status of the individual. Hyponatremia can be divided into hypovolemia, euvolemia, and hypervolemia categories. (See Hyponatremia algorithm, Figure 9–18 .)

Comments

Spurious hyponatremia may be produced by severe lipemia or hyperproteinemia if sodium analysis involves a dilution step.

Many guidelines recommend a correction factor, whereby the serum sodium concentration decreases by 1.6 meq/L for every 100 mg/dL (5.56 mmol/L) rise in plasma glucose above normal, but there is evidence that the decrease may be greater when patients have more severe hyperglycemia (> 400 mg/dL or 22.2 mmol/L) and/or volume depletion. One group has suggested that, when the serum glucose is > 200 mg/dL, the serum sodium concentration decreases by at least 2.4 meq/L.